Right now, I am just trying to get the things together so I can get it on the road. Eventually it will be doing some mudding, and some trail riding, but nothing crazy. It is a mildly built 400. The motor came with a 600cfm edelbrock 1405 with manual choke, but I do not want to use it. I also have a Motorcraft, by Holley, 4180c, that came off of an 84 bronco, but not sure I really want to use that either.
I would use the Avenger, but check primary jet size against the 4180. Use whichever jets are smaller. If you are running an automatic, you might need the ball for the kickdown to mount to. The Avenger should have the hole in the linkage, for the ball. I bought my ball/stud at NAPA.
In my experience with ANY Holley carb, there is nothing you can't fix on them. If it is varnished, disassemble it and throw it in a can of carb dip. the main body won't fit in the gallon pail. Find something that is does fit in and transfer the dip to that container then drop the main body in it. What elevation are you at? At 8000' here i know that Holley doesn't make a small enough power valve so you have to restrict the flow in the metering block with a strand of copper wire and drop three jet steps. For most off road driving you can adjust the float bowls down to keep fuel from spilling out of the vent tube. If it stutters off idle you may need a bigger accelerator pump. This can be made worse with the installation of a carb spacer.
Just saw that Sparta IL is at 528 feet so out of the box i bet that carb would be fine.. just make sure is is in good working order and CLEAN! Make sure someone hasn't put a screw in the vacuum secondary linkage. Also, they come with a pretty heavy spring in the vacuum secondary. Get the secondary spring kit and play around with it.
Heard good stuff about the Avengers. In the classic Mustang world a lot of people preferred Holleys for tweaking more for a little more power, but Edelbrocks for better reliability. At least that's what I've gathered.
I have a Holley 600cfm on mine (which is a bit of overkill for the 289) and I admit I am constantly having to tweak that thing to make it run right depending on the weather and humidity.